Articles in English are invariable. That is, they do not change according to the gender or
number of the noun they refer to, e.g. the boy, the woman, the children
'The' is used:
1. to refer to something which has already been mentioned.
Example: I met a boy in the street.
the boy was so hungry, so i gave him some biscuits.
2. when both the speaker and listener know what is being talked about, even if it has not been mentioned before.
Example: 'Where's the library?'
'It's on the first floor.'
3. in sentences or clauses where we define or identify a particular person or object:
Examples: The girl who wrote this story is clever.
'Which blouse did you choose?' 'The red one.
My house is the one with a blue door.'
4. to refer to objects we regard as unique:
Examples: the sun, the moon, the world
5. before superlatives and ordinal numbers:
Examples: the highest building, the first page, the last chapter.
6. with adjectives, to refer to a whole group of people:
Examples: the Indians, the old, the poor, the rich
7. with names of geographical areas and oceans:
Examples: the Caribbean, the Sahara, the Atlantic
8. with decades, or groups of years:
Example: she grew up in the seventies